National Geographic News asked Hendrik Poinar, a molecular evolutionary geneticist and biological anthropologist at the Ancient DNA Centre at McMaster University in Hamilton, Ontario, if we might soon see the gigantic land mammals roaming the steppe again. Poinar will speak about the emerging technology at the TEDx Conference on DeExtinction in Washington this month.

"People were painting pictures of woolly mammoths in caves in France 35,000 years ago, so we have this amazing history with them," Poinar said.

Poinar's team isolates DNA and proteins from fossils and preserved remains, and then uses sophisticated sequencing and analysis tools to answer questions about species extinctions, evolution, and even the spread of infectious diseases. Poinar has tested relatively well-preserved samples from mammoth carcasses uncovered in the Yukon and Siberia. The mammoth remains had been entombed in the permafrost (permanently frozen ground), so degradation of their DNA had been slowed over time, Poinar explained.

New Gene Tools

In 2006, Poinar's lab began to map large sections of the mammoth's genome, aided by new high-input DNA sequencers, which can quickly analyze millions of fragments. This is important, because even the most well-preserved mammoth specimens have DNA strands that have fallen apart into countless smaller sequences, since the complex molecule is highly susceptible to decay (Poinar said DNA starts breaking down as soon as a living thing dies.)

"You'll never really create an exact genome because when you have short fragments there are no good ways to know how many repeats of sequences there are," said Poinar. But scientists can compare the fragments to each other to find overlapping areas, and then piece together much of the strand. Then, they can map those regions against the DNA of the closest living relative of the mammoth—the Asian elephant.

"We can in theory use that information to modify existing chromosomes with what we imagine to be mammoth substitutions," said Poinar. The result would be an elephant-mammoth hybrid, and such a creature could theoretically be implanted into the womb of a mother elephant. Get the formula right, and the offspring might be "a mammoth in the eye of the beholder," said Poinar.

Raising Big Questions

Poinar asked why scientists would want to do that in the first place. "Is it because we have this ability, to push the boundaries of what's possible for the sake of innovation?" he asked.

Poinar added, "Would it give conservation movements something new to generate excitement, or does it generate apathy, so people ask 'why do we need to care about saving them in the wild if we can bring them back?'"

Poinar said he thought parts of Siberia could support reborn populations of mammoths, and that they would likely be able to survive, even in a warming climate, because they had existed across such a wide range.

"That doesn't mean it's the right thing to do," Poinar added. "As much as the kid in me would love to see these fantastic species plundering across the north, it's hard to see a reason why we should unless we think this technology could give us tools for conservation." He explained that the real win would be adapting such techniques to bolster the numbers of current endangered species, such as mountain gorillas.

—Brian Clark Howard

Photograph by Joel Sartore, National Geographic

Gastric-Brooding Frog

In this file photo, a tiny froglet can be seen in the mouth of its mother, a gastric-brooding frog. In this novel form of parental care, the female swallowed her fertilized eggs. Her stomach then stopped producing acid, becoming a makeshift womb. Later, she regurgitated fully formed froglets.

Two species of gastric-brooding frogs made their homes in creeks in a relatively small area of tropical forest in Queensland, Australia, the southern gastric-brooding frog (Rheobatrachus silus) and the northern gastric-brooding frog (Rheobatrachus vitellinus). The species were discovered in 1973 and 1984, respectively, but by the mid-1980s they had both disappeared.

Biologists aren't sure why the frogs went extinct, but they suspect habitat degradation, pollution, and possibly disease, including chytrid fungus.

A number of writers have suggested that the frogs' unique lifecycles could have taught us valuable insights about acid production and suppression, possibly leading to relief for those who suffer from ulcers and other maladies.

A few specimens of gastric-brooding frogs are preserved in Australian museums, leading scientists to ponder whether the animals could be reborn. Ben Novak, a former student of Poinar and another speaker at the TEDx Conference on DeExtinction, thinks it's possible.

"Museum tissue DNA can be rather low quality," Novak cautioned. But, he said, new gene sequencing technology that has become available in the past three years has made it possible to start getting better results. He pointed to recent research by another lab on a rat specimen that had died 70 years earlier. "They got really good coverage of almost an entire genome," said Novak.

"Any taxidermied or museum-preserved tissue can yield a whole genome with a piece of tissue the size of a pin head," said Novak. The key to deciperhing that genome is spending the money to run the samples through the sequencers many times and mapping the results against a related species, he said.

In the case of the gastric-brooding frogs, there may be usable relatives, even if they don't swallow their young. One concern, Novak cautioned, is that there is a risk of damaging or destroying the small amount of preserved material to extract DNA.

Photograph from ANT Photo Library/Science Source

Passenger Pigeon

The passenger pigeon (Ectopistes migratorius) numbered in the billions in North America during the 19th century, but by the early 20th century, it had gone extinct, thanks to relentless hunting and habitat pressure. Now, geneticist Ben Novak and a handful of other scientists are working on bringing it back.

Novak explained that he has worked with three museum specimens of passenger pigeons, and has been able to get "half of the entire genome from any random selection of the tissue."

"Museum tissue DNA can be rather low quality," Novak cautioned. But, he said, new gene sequencing technology that has become available in the past three years has made it possible to start getting better results. He pointed to recent research by another lab on a rat specimen that had died 70 years earlier. "They got really good coverage of almost an entire genome," said Novak.

"Any taxidermied or museum-preserved tissue can yield a whole genome with a piece of tissue the size of a pin head," said Novak. The key to deciperhing that genome is spending the money to run the samples through the sequencers many times and mapping the results against a related species, he said.

Novak is currently moving to Santa Cruz, California, where he will join Beth Shapiro's lab. Together, they will evaluate a cache of samples, choose the most promising, and then attempt to sequence the whole genome.

According to Novak, there is a reasonably good surrogate to the passenger pigeon in the form of the extant band-tailed pigeon, which he is working on sequencing. Still, the task of mapping fragments of passenger pigeon DNA won't be easy.

"Our data indicate that the entire passenger pigeon genome is in the dataset, but we won't be able to assemble and map it all because of degradations and evolutionary divergence, and it could be that some sequences don't map at all to the band-tailed," said Novak, another speaker at the TEDx conference on DeExtinction.

Photograph by Joel Sartore, National Geographic

Dodo

A dodo skeleton sits opposite a reconstructed model of the extinct bird in the National Museum of Wales, Cardiff. The dodo (Raphus cucullatus) is an extinct flightless bird that once lived on the island of Mauritius in the Indian Ocean.

The last widely accepted sighting of the dodo was in 1662, less than one hundred years after the bird was first described by Dutch sailors. The large birds were preyed upon by sailors and the invasive animals they brought with them. Because Mauritius had few predators, the birds had few defenses.

A few dodo specimens were collected by early European explorers and remain in museums today, at least one with soft tissue. Recent excavations of swamps on the island have also turned up "fresh" fossil remains.

"Our work shows that as long as you have any type of skin or muscle preserved you should be able to get the entire genome out of it, with some degree of quality," said Novak.

He added that the dodo is an extinct type of pigeon, so there should be some fairly close species for mapping DNA (and possibly to serve as a surrogate parent). Some studies suggest the Nicobar pigeon is the closest living relative.

Photograph by Fox Photos/Getty Images

Pyrenean Ibex

The Pyrenean ibex (Capra pyrenaica) was a wild goat native to the Iberian Peninsula. It went extinct in 2000 due to hunting and competition from domestic animals.

Before the species expired, scientists collected DNA from one of the last living females and froze it, to reduce degradation. Over several years, researchers tried to clone back the species, using a related goat as a surrogate. One of the clones was born in 2009, but it lived for only seven minutes.

The project highlighted a number of the challenges with trying to bring back extinct species, including the need to create breeding pairs and the importance of genetic diversity (neither obstacle was overcome in this case). Scientists may not need to create a large number of individuals to establish diversity, Novak said, if they can work with DNA from several unrelated individuals so they can do some mixing and matching.

Photograph by Simon Littlejohn, Foto Natura/Corbis

Carolina Parakeet

The Carolina parakeet (Conuropsis carolinensis) was the only native species of parrot in the eastern United States, having ranged from southern New York to the Gulf of Mexico, and as far west as Wisconsin. The gregarious parakeets lived in mature forests along rivers, where they feasted on fruits and nuts.

The population of these birds declined through the 19th century, however, as agricultural expansion destroyed habitat, and many of the birds were collected for their feathers and the pet trade. Introduced honey bees may also have outcompeted them for nests. Finally, many orchard managers poisoned Carolina parakeets because they could damage crops. The last known wild Carolina parakeet was killed in Florida in 1904, and the last captive bird died at the Cincinnati Zoo in 1918.

There are a number of Carolina parakeet specimens in museums around the world, including 720 skins, 16 skeletons, and several remains of eggs. According to a study of mitochondrial DNA from such materials, their closest living relatives include the sun parakeet, the golden-capped parakeet, and the nanday parakeet.

According to Novak, this is good news for those who might try to bring back the Carolina parakeet. In contrast, "the elephant bird of Madagascar might be a phenomenal bird to return to its ecosystem, but there is not a bird on the planet that can lay an egg large enough, so unless you can grow an embryo in a test tube an elephant bird is impossible," he said. "A giant sloth is also impossible, because a living sloth cannot birth one."

Further, when it comes to extinct large animals like the mammoth, there may be an additional problem. "To get a successful birth of a mammoth you might have to use one hundred surrogate mother elephants, but if you are doing that why aren't you making one hundred elephants [because elephant populations have declined dramatically in recent years]?" asked Novak.

"It's going to be easier to work with animals in which their surrogate is very common and not politically controversial," added Novak. "There are a host of parrots and parakeets that people breed privately, and those are perfect for using without taking away from conservation efforts."

Photograph by Julie Dermansky,Getty Images

Woolly Rhinoceros

The woolly rhino (Coelodonta antiquitatis) is another species of Pleistocene megafauna that was depicted in prehistoric cave art, like the woolly mammoth. There is considerable debate about precisely when the woolly rhino went extinct, but it is thought to be around the end of the ice age, roughly 10,000 years ago.

A few woolly rhino carcasses have been recovered from the permafrost in Siberia, and one highly intact one was pulled from a tar pit in Starunia, Poland. Some DNA analysis has been done, and a study published in Molecular Phylogenetics and Evolution concluded that the woolly rhino's nearest living relative is the Sumatran rhino. Unfortunately, that species is barely hanging on itself, and is listed as critically endangered by the International Union for Conservation of Nature (IUCN).

Asked about the feasibility of bringing back a woolly rhino, Poinar wasn't optimistic. "The problem with the woolly rhino is the number of samples is very limited. For every hundred mammoths you find you might find one woolly rhino," he said.

So the challenge is likely to be tougher than with the mammoth, although some of the right elements are in place, namely body parts and a potential living surrogate.

Illustration by Charles R. Knight, National Geographic

Moa

The moa were a group of nine species (in six genera) of large flightless birds that lived in New Zealand. The largest, Dinornis robustus and Dinornis novaezelandiae, dwarfed the modern ostrich, reaching a height of 12 feet (3.6 meters) and weight of 510 pounds (230 kilograms).

Moa disappeared by the year 1400, after being hunted by the Maori, and after their habitat was disturbed for farmland.

According to Novak, moa might be a candidate for rebirth because they "had a lot of large, good bones for scientists to work with. If we can get genes out of mammoth femurs that are 20,00 years old we can get DNA out of anything that died in the last thousand years." Novak added that bones don't yield as many formerly living cells per square inch as soft tissue, since much of their composition is mineral, although they still have potential as a source for DNA.

In the case of moa, in addition to thousands of bones, scientists have also found preserved soft tissue, in the form of skin, muscle, and feathers, thanks to dessication in New Zeland's semiarid Central Otago region.

Still, the moa's giant size might make it difficult for a surrogate to lay a large enough egg.

Photograph by Frans Lanting, National Geographic

Thylacine (Tasmanian Tiger)

Roughly the size of a large dog, the thylacine or Tasmanian tiger (Thylacinus cynocephalus) was a striped carnivorous marsupial that lived on Australia, Tasmania, and New Guinea. Tasmania was its last stronghold, but the animal was pronounced extinct in the 1930s. Loss of habitat and introduced dogs likely played a role, although most biologists point to hunting as a primary cause.

According to Novak, it will be challenging for scientists to bring back the thylacine, "because it is more diverged from its living counterparts." The Tasmanian devil and numbat are thought to be the closest relatives, although both are considerably smaller.

Still, that hasn't stopped scientists from trying. In 2008, Andrew Pask at the University of Melbourne, Australia, extracted thylacine DNA from four 100-year-old samples, including a pelt and three infant animals stored in alcohol. Pask's team isolated a short sequence, inserted a marker, and then injected it into a mouse embryo. They proved that the gene from the extinct species could still be expressed.

At the time, Pask told the New Scientist that he didn't expect to be able to clone an entire thylacine, since known samples have badly degraded DNA. In April 2012, Pask published additional research showing that the thylacine, when alive, suffered from low genetic diversity.